Banknotes, securities, certificates, brand products, personal authentication media, and the like are expected to be forgery-proof. To this end, laminate (s) having an excellent forgery prevention effect may be attached to those items as appropriate.
Most of the laminates include a microstructure such as a diffraction grating, a hologram, a lens array, and a scattering structure. These microstructures are hard to analyze. And, to manufacture the laminates including one of these microstructures requires costly manufacturing equipment such as an electron beam lithography system. In consequence, the laminates can present an excellent forgery prevention effect.
Each of these laminates usually includes a relief structure forming layer with a principal surface that includes the microstructure, and a reflective layer provided thereon. In this case, the reflective layer in the form of a pattern may be provided only on part of the principal surface so as to further enhance the forgery prevention effect. For instance, a pattern in the form of micro characters that emit diffracted light is obtained by providing the reflective layer on the principal surface such that the contours of the reflective layer form the micro characters.
PTL 1 adopts the following method in order to form a reflective layer with high positional accuracy.
First, a relief structure forming layer is prepared which includes a “first region” that is provided with an indented structure having a high depth-to-width ratio, and a “second region” that is either flat or provided with an indented structure having a lower depth-to-width ratio. Next, a metal reflective layer is formed at a uniform surface density on this relief structure forming layer with a vacuum deposition method. Thereafter, a material having resistance to an etchant to etch the metal reflective layer is deposited at a uniform surface density with the vacuum deposition method, thus providing a “second layer”. Subsequently, a laminate thus obtained is subjected to an etching treatment.
Of the “second layer”, a portion corresponding to the “first region” is permeable to the etchant because a deposited film thereon is either a discontinuous film or a porous film, which is attributed to the indented structure having the high depth-to-width ratio. On the other hand, of the “second layer”, a portion corresponding to the “second region” is not permeable to the etchant because the portion is either flat or provided with the indented structure having the lower depth-to-width ratio, and thus a deposited film thereon is a uniform continuous film.
Accordingly, by immersion of the obtained laminate in the etchant, only the portion of the metal reflective layer corresponding to the “first region” can be etched and removed. In other words, the metal reflective layer can be formed only in the “second region”.
This manufacturing process has advantages in light of cost and productivity from the viewpoint that the metal reflective layer can be formed with high positional accuracy while requiring no exposure processes on a photosensitive layer.